The present invention first relates to a balloon catheter, in particular for invasive radiotherapy, with a catheter shaft for introducing aerobe, having a first, outer balloon and having a second, inner balloon, disposed inside the outer balloon, the inner space of the second, inner balloon connecting with a channel for connection to a media inlet, and intermediate space between the first, outer balloon and the second, inner balloon connecting to a channel for connection to a media storage unit. In addition, the invention also relates to an applicator, in particular for invasive radiotherapy, having a balloon catheter, with a catheter shaft for introducing a probe, having a first, outer balloon made of a flexible, non-extendible material and a second, inner balloon made of a flexible, extendible material disposed inside outer balloon, additionally having an inside space of the second, inner balloon, which is connected via a connection channel at least temporarily with a media inlet, and additionally having an intermediate space between the first, outer balloon and the second, inner balloon, which is connected via a connection channel at least temporarily with a media storage unit.
In invasive radiation therapy of tumors, there exist different methods for irradiating the tumor, or for irradiating the tumor bed after lumpectomy has been performed. For this, access to the tumor or to the remaining tumor bed must be created. This access, which is temporary, can be made possible by means of a balloon catheter, which can function as a type of place holder, especially in the case of irradiation of a tumor bed.
Most frequently, the balloon catheter, which is folded together, is put in place via a biopsy channel created therefor. The balloon is subsequently filled with a medium, so that it assumes its defined shape. Such a balloon catheter is disclosed, for example, in U.S. Pat. No. 5,621,780 A.
An isotonic saline solution is often used as a filling medium. This is used first and foremost in order to minimize the risk to the patient in the case of a balloon rupture due to pressurized filling medium, since water can hardly be compressed. In addition, a physiological saline solution can better assure the dimensional stability of the balloon than gases, for example.
In addition to access to the tumor bed, the balloon catheter has the task of providing a defined shape, preferably a spherical shape, to the tumor bed that is dimensionally unstable. Other geometries are also possible, however. A uniform irradiation of the surrounding tissue will thus be made possible without complex irradiation planning.
In this method, for irradiation planning, it is important to know whether the actual shape of the balloon is also the desired or necessary shape. The shape may deviate from the defined basic form due to particular local features, especially in balloons which are made of extendible material.
An increase in internal pressure due to the introduction of additional media does not offer a solution here, since the balloon would only be further extended, increasing the risk of a balloon rupture.
If a deviation in shape is not noticed, because of different distances, erroneous irradiation of the surrounding tissue will occur.
The application of “solid applicators” would be ideal here. The solid structure used would ideally suppress the surrounding tissue and thus make possible a molding of the tissue around the applicator. Solid applicators guarantee a stable arrangement during the irradiation. However, based on their primary property, they are not suitable for application in the case of fractionated irradiation, since they cannot be removed in a minimally invasive manner after the irradiation.
In order to assure the balloon shape, this shape is tested in practice with different imaging methods after the balloon is placed in the body. After the irradiation, which may extend over several irradiation sessions, the filling medium can be aspirated and the balloon catheter can be removed through the biopsy channel.
Techniques such as computed tomography (CT) or ultrasound are used very frequently for visualizing the balloon catheter in the patient. In this case, however, imaging is made difficult due to the special properties of the balloon catheter. Once the balloon is filled, usually with an aqueous solution, for shaping, the balloon can barely be distinguished from the surrounding tissue. This makes imaging by CT or ultrasound difficult. Air would be rather well suitable for visualizing. Based on its high compression, which is required for dimensional stability, however, this medium is associated with an elevated risk for the patient. Therefore, materials or structures that absorb x-rays and are found in or on the balloon walls must be used in CT in order to make the balloon catheter visible. There is also the possibility of filling the balloon with a contrast agent or a water/contrast agent mixture.
In addition to the radiation load due to CT that is based on its principle, another undesired side effect results for the patient. For imaging, it is necessary that x-rays are absorbed. This also means, however, that a part of the x-ray radiation is be absorbed during therapy. In order to compensate for this, either the power of the x-ray source or the irradiation time must be increased.
A change in the course of treatment could be a solution to the problem. Thus, for example, the balloon could first be filled with air or a contrast agent. After positioning and checking the shape, this medium will be replaced by the actual filling medium for the irradiation. This exchange, however, poses the risk that the positional relationships will change again. With the conventional use of contrast agent, after this exchange has been made, it is difficult to say how complete this exchange was or whether there are any highly concentrated accumulations of contrast agent somewhere in the balloon catheter. The effect would be a non-uniform irradiation of the tumor bed, since residues of the contrast agent locally absorb the x-ray radiation in a limited manner. A complete killing of the tumor cells is therefore not assured.
In another context, a balloon catheter is known from WO 99/04856 A1, with which the intensity of radiation that is emitted from a radiation source and strikes the tissue to be treated can be adjusted. The known balloon catheter has a catheter shaft as well as a first, outer balloon and a second, inner balloon disposed inside the outer balloon. An intermediate space is created between the inner balloon and the outer balloon in order to keep constant the distance between the balloons, and thus the volume of the intermediate space will be maintained constant. A liquid introduced into the intermediate space has the task of absorbing radiation. However, with this known solution, the above-named problem still cannot be solved.
Another solution for a balloon catheter with two balloons lying one inside the other is described in US 2005/0080313 A1. The two balloons are joined together over large regions in this known solution. The two balloons are detached from one another only at specific sites, so that a gap is formed into which a medium can be injected. In this way, individual regions of tissue may be excluded from irradiation. Also, with this solution, it is still not possible to solve the above-named problems with respect to placement of the balloon catheter.